1. Field of the Invention
The present invention relates to an image transmitting apparatus, an image receiving apparatus, and an image transmission system which transmit or receive image data.
2. Related Art
In order to deal with high resolution and high quality image data, it is necessary to transmit massive image data. This massive data transfer in recent year causes an EMI problem.
Many data transmission techniques are proposed to cope with EMI, such as RSDS (Reduced Swing Differential Signaling), mini-LVDS (Low Voltage Differential Signaling), CMADS (Current Mode Advanced Differential Signaling), whisper BUS, Mobile-CMADS, MSDL (Mobile Shrink Data Link), MPL (Mobile Pixel Link), and MVL (Mobile Video Interface). Some papers are reported in the Society for Information Display: A Lee's paper concerning RSDS (refer to “Integrated TFT-LCD Timing Controllers with RSDS Column Driver Interface, SID Digest 6.2, 1999”), a Yusa's paper concerning CMADA (refer to “High-Speed I/F for TFT-LCD Source Driver IC by CMADS, SID Digest 9.4, 2001”), and a McCartney's paper (refer to “Whisper BUS: An Advanced Interconnect Link For TFT Column Driver Data, SID Digest.9.3, 2001”). In addition, a comparative article has collectively discussed on introductions of serial interfaces for cellular phone (refer to “A revolver type promotes a serial interface. The wire count is reduced to 1/10 or less”. Nikkei electronics, No. 3.15 in 2004, pp. 128-130”).
Furthermore, cellular phones have several extensions of the serial interfaces: Mobile-CMADS, MSDL, MPL, and MVI. In the extensions, circuit improvements successfully (but fortunately) suppressed EMI since the amount of pixels is still small at the present time. However, these are temporary remedy. As the amount of pixels will increase further from now on, the size of data will rapidly increase too. This rapid increase implies that the circuit is requested to operate at higher frequency, and cost of the circuit is becoming more intolerant. Therefore, the improvements of circuit will reach critical limit in the near future.
Power consumption is an important factor in electronic devices especially in the case that device is power-supplied by a battery in cellular phones. In addition, higher speed operation of circuits is not desirable. Hence, we need another new technology, but the technology should be consistent with the conventional technology. This means that solutions to be investigated should be “add-on approach” based on the conventional circuit-related improvements. Considering this strategy, compression of data size and reduction of data transition will be cited as conventional technology relating to the present invention. These will be explained below.
Japanese Patent Laid-Open No. 2003-366107 includes the transition reducing technology such as an alternative bit inversion method, and the size reducing technologies such as a Huffman coding, an one-dimensional compressing method, and an arithmetic compression method. This official gazette reported that size of data reduction is not always attained to ½, and its data size changes heavily depending on data itself. This dependency requests an adjustment of transmission frequency according to data size in order to transfer data without loss. An extra control circuit is not desirable in order to implement the adjustment.
In addition, Japanese Patent Laid-Open No. 2002-202760 includes a technology, which reduces data transition using popular bus inversion technique: when majority of data changes, original data is intentionally bit-inverted to reduce data transition. These official gazettes treat data as a “general number” to be transferred in a bus. A property of image data is not utilized well. For this reason, compression ratio is not so high.
Japanese Patent Laid-Open No. 2000-152129 includes a technology of utilizing addition and subtraction to reduce data transition. In this official gazette, a numerical conversion reduces transition count: for example, an operation “add one” is such a conversion. This conversion transforms a transition “0000 to 1111” to a transition “0001 to 0000”, which reduces transition count (4 transitions to 1 transition). Since this official gazette also treats “general data”, not specialized for image data, image data cannot be processed effectively from the aspect of utilization of statistical property of image.
In addition, an FV coding method is known, which performs bus inversion with dynamic monitoring of data frequency (refer to “Jun Yang, Rajiv Gupta, FV Encoding for low-power Data I/O, IEEE, and ISLPED 2001). This method also does not intentionally utilize the statistical property of image as data.
Now, survey will proceed to the technologies to utilize statistical property of image. Japanese Patent Laid-Open No. 2003-44017 includes a method to reduce size of data to be transferred. When a current data has same value as a 1H-previous data, the re-usage of saved 1H-previous data don not request the transfer of current data. This non-transmission works equivalently as a reduction of data size. However, since a probability in an actual image to have same value as 1H-previous is ten to twenty percent on average, the above non-transmission attains at most twenty percent reduction. Hence, it is impossible to obtain so large enough effect that EMI noise is fully reduced.
In addition, a VDE method is proposed, which reduces EMI noise using “1H” correlation of an image (refer to Japanese Patent Laid-Open No. 2000-20031, U.S. Pat. No. 6,344,850, and a paper of “Haruhiko Okumura et al., Vertically Differential EMI Compression Method for High Resolution LCDs, SID I DRC 2003”). In these reports, “1H” prediction, “1V” prediction, and a spatial predictor are so simple that its resultant performance is insufficient. In addition, the VDE method simply transfers differential data as it is, and the VDE method has no channel coding to reduce a transition count on a channel. For this reason, good performance can be achieved only when correlation is extremely high like a PC screen artificially generated. Hence, its performance is not good for natural images such as a TV screen.
ISO standard FCD14495 is a popular technology known as JPEG-LS (lossless) at the present time. JPEG-LS is one of most advanced data compression technology without data loss (lossless). The JPEG-LS technology uses DPCM (Differential Pulse Code Modulation). MED (Median edge detector) and GAP (gradient-adjusted predictor) are well known as DPCM technology related to image data. As GAP needs 2H memory (memory for two horizontal lines) and hardware circuit size is large, MED is discussed to use as DPCM hereinafter because MED needs only 1H memory. But, prioritizing of area-efficient implementation may select another choice if necessary, because the other predictor with rather inferior performance may have smaller hardware.
MED has been further improved in recent years. There is a modified MED technology to improve performance with diagonal edges (refer to a paper of “Jiang et al., Revisiting the JPEG-LS prediction scheme, IEE Proc. Visual Image Signal Process, Vol. 147, No. 6, December 2000, pp. 575-580).
In addition, there is another modified MED technology to improve performance with different prediction formula (refer to papers of “Grecos et al., Two Low Cost Algorithms for Improved Diagonal Edge Detection in JPEG-LS, IEEE Transaction on Consumer Electronics, Vol. 47, No. 3, August 2001, pp. 466-473”, and “Jiang et al., “Toward improved prediction accuracy in JPEG-LS”, SPIE Optical Engineering, 41(2) 335-341 (February 2002)”). Yet another modified MED with higher performance is proposed (refer to a paper of “Edirisinghe, Improvements to JPEG-LS via diagonal edge based prediction, Visual Communications and Image Processing 2002, Proceedings of SPIE, Vol. 4671 (2002)”. All these conventional MEDs are used for the purpose of data compression. They are not used for the different purposes: reduction of EMI noise and reduction of wiring count.
Next, conventional technologies to utilize image entropy will be explained to quickly survey related technologies, because they are generally helpful to understand the present invention. Several data compression technologies are known, which utilize entropy in order to reduce size of encoded codes. These include technologies such as Golomb codes, arithmetic coding, and Huffman coding, (David Salomon, Data Compression, 3rd Edition, 2004, Springer-Verlag).
In recent years, there are other two technical directions. One is an idea of reducing a transition count in data. Another is an idea of reducing amplitude of signal. First, a survey will be started from technology of transition count reduction. There are three technologies concerning EMI improvement for DVI (Digital Visual Interface, DVI Revision 1.0, Apr. 02, 1999, Digital Display Working Group, http: //www.ddwg.org). A first is “Chromatic encoding” technology by Cheng et al. (We-Chung Cheng and Massound Pedram, Chromatic Encoding: a Low Power Encoding Technique for Digital Visual Interface, IEEE DATE 2003 session 6.3) (technology added to U.S. Pat. No. 5,974,464). A second is “Differential Bar Encoding” technology by Bocca et al. (Alberto Bocca, Sabino Salerno, Enrico Macii, and Massimo Poncino, Energy-Efficient Bus Encoding for LCD Displays, GLSVLSI'04). A last is “Limited Intra-Word Transition Codes” (Sabino Salerno, Alberto Bocca, Enrico Macii, and Massimo Poncino, Limited Intra-Word Transition Codes: An Energy-Efficient Bus Encoding for LCD Display Interfaces, IEEE/ACM ISLPED 2004, session 7.4). As shown above, three variations to reduce transition count are already known.
On the other hand, there is a multi-value image entropy coding (MVIEC) as technology of using entropy to deduce amplitude (U.S. Pat. No. 6,633,243: Hisashi Sasaki, Tooru Arai, Masayuki Hachiuma, Akira Masuko, and Takashi Taguchi, Multi-Valued Image Entropy Coding for Input-Width Reduction of LCD Source Drivers, SID Asia Dispiay/IMID 2004).
However, considering further increase in the amount of pixels, the conventional multi-value image entropy coding cannot fully reduce signal amplitude yet. Hence, further reduction of power consumption is requested.